The present invention generally relates to a method for making hollow metal ball bats. More particularly, the present invention relates to a method for making metal ball bats using a pilger mill, a draw bench, and a rotary swager in combination to obtain a perfect roundness and wall uniformity for the handle and taper sections of the bat.
The methods of manufacturing ball bats and improvements in the design and materials have been the subject of numerous patents over the years, most directed to ball bats used in games of baseball and softball. The baseball bat was initially made of wood, and to this day, ball bats used in professional baseball leagues are exclusively made of hard woods. However, over the years, there has been a great increase in the number of ball bats to meet the demand for the increasingly popularity of the sport, including semi-professional, college, little league and baseball and softball organized leagues. Metal bats have been increasingly used as substitutes for wooden bats because of their light weight, and while metal bats typically cost more than wooden bats, they have the great advantage of lasting longer, and hence of costing less in the long run.
An early approach, such as disclosed by U.S. Pat. No. 1,611,858 to Middlekauff, was to make a ball bat from tapered steel tube, formed by a rolled tapered sheet with mating edges joined along a seam to form the tube. However, it soon became apparent that seamless lightweight metal tubing, such as aluminum or titanium, was preferred. This is due to the fact that the metal bat should closely resemble the operating characteristics of a wood bat, so as to exhibit the weight distribution, feel, and sound of the wood bat when hitting the ball.
Early efforts to develop aluminum bats included the approach of swaging down the length of a cylindrical extrusion or tube. The extrusion is swaged down by striking or contacting the member with clapping hammers, which repetitively strike the outer surface of the extrusion. The striking motion is perpendicular to the longitudinal axis of the tube which causes the exterior diameter of the tube to be reduced, thus forming an intermediate tapered portion, or trumpet, and handle end of the ball bat. While generally having a smooth outer surface, it was discovered that the interior surface of the ball bat formed by this method was less than smooth, and could have cracks or fractures running parallel to the longitudinal axis of the ball bat. Of course, these cracks weakened the bat and reduced its longevity. Moreover, the swaging process did not result in a uniform wall thickness of the tapered or trumpet section. The increased wall thickness added to the weight of the bat, and did not contribute to the strength of the bat as it displaced the center of gravity of the bat away from the hitting end of the bat.
In an effort to overcome these disadvantages, Ploughe et al., as disclosed in U.S. Pat. No. 5,626,050, developed a methodology of forming a hollow metal ball bat using a cold pilger process. An aluminum tube blank is fixed into a “pusher”, the pusher having a cylindrical opening having a diameter slightly larger than the outer diameter of the tube blank. The pusher and threaded extension rod are then used to advance the aluminum tube blank into a pilger mill, also referred to as a reducing rolling mill. This reduces the aluminum tube to form the handle section and the tapered section, and thereby form the bat-shaped stock for fabricating a hollow metal ball bat.
However, this procedure also has its disadvantages. The use of an adapter, a pusher, and threaded extension rod has been found to be unsafe, inefficient, and time consuming. This process has also used a partial, typically half, ring die set, which generates a significant amount of heat when reducing the tubes. Although the use of an internal mandrel is useful to control the tube wall thickening as compared to the swaging process, it significantly added to the metal working costs and greatly increased the stress in the machinery used to reduce the outside diameter of the tube.
U.S. Pat. No. 6,735,998 to Mitchell appreciated the disadvantages of forming hollow metal ball bats using either a swaging or a cold pilgering process. In order to overcome these disadvantages, Mitchell proposed a process for forming ball bats by the use of drawing a blank only partly through a contoured die, or a succession of contour dies. By only reducing the diameter of essentially only a select length of the tubular metal blank by the use of tension plied to pull the metal blank in a die or a succession of dies, Mitchell asserted that an intermediate annealing step could usually be eliminated and a thinner tube wall in the handle and transition for trumpet sections of the ball bat obtained.
The inventor has discovered that each of the swaging, cold pilgering, and draw processes present both advantages as well as disadvantages. Accordingly, there is a continuing need for a process for manufacturing a hollow metal ball bat utilizing a combination of processes so as to synergistically create a better ball bat and an improved manufacturing process. The present invention fulfills these needs and provides other related advantages.